Spectroscopic search for new SW Sextantis stars in the 3-4 h

[Abridged] We report on time-resolved optical spectroscopy of ten non-eclipsing nova-like cataclysmic variables in the orbital period range between 3 and 4 hours. Of the ten systems so far observed, HL Aqr, BO Cet, AH Men, V380 Oph, AH Pic, and LN UMa are

Mon.Not.R.Astron.Soc.000,(2006)Printed4February2008

A(MNLTEXstyle lev2.2)

SpectroscopicsearchfornewSWSextantisstarsinthe3–4

hourorbitalperiodrange–I.

arXiv:astro-ph/0611829v1 27 Nov 2006

1,2 23

P.Rodr´ guez-Gil,L.SchmidtobreickandB.T.G¨ansicke1

2European

InstitutodeAstrof´ sicadeCanarias,V´ aL´acteas/n,LaLaguna,E-38205,SantaCruzdeTenerife,Spain

SouthernObservatory,Casilla19001,Santiago19,Chile

3DepartmentofPhysics,UniversityofWarwick,CoventryCV47AL,UK

Accepted2006.Received2006

ABSTRACT

Wereportontime-resolvedopticalspectroscopyoftennon-eclipsingnova-likecata-clysmicvariablesintheorbitalperiodrangebetween3and4hours.Themainobjectiveofthislong-termprogrammeistosearchforthecharacteristicSWSextantisbehaviourandtoeventuallyquantifytheimpactoftheSWSexphenomenononnova-likesattheupperboundaryoftheorbitalperiodgap.

Ofthetensystemssofarobserved,HLAqr,BOCet,AHMen,V380Oph,AHPic,andLNUMaareidenti edasnewmembersoftheSWSexclass.WepresentimprovedorbitalperiodmeasurementsforHLAqr(Porb=3.254±0.001h)andV380Oph(Porb=3.69857±0.00002h).BOCetandV380Ophexhibitemission-line aringwithperiodicitiesof20minand47min,respectively.TheHαlineofHLAqrshowssigni cantblueshiftedabsorptionmodulatedattheorbitalperiod.SimilarlytotheemissionS-waveofthehigh-inclinationSWSexstars,thisabsorptionS-wavehasitsmaximumbluevelocityatorbitalphase～0.5.WeestimateanorbitalinclinationforHLAqrintherange19 <i<27 ,whichismuchlowerthanthatoftheemission-dominated,non-eclipsingSWSexstars(i～60 70 ).Thisgivesrisetotheinterestingpossibilityofmanylow-inclinationnova-likesactuallybeingSWSexstars,butwithaverydi erentspectroscopicappearanceastheyshowsigni cantabsorption.Theincreasingblueshiftedabsorptionwithdecreasinginclinationpointstotheexistenceofamassout owwithsigni cantverticalmotion.

ThissixnewadditionstotheSWSexclassincreasethepresenceofnon-eclipsingsystemstoaboutonethirdofthewholeSWSexpopulation,whichthereforemakestherequirementofeclipsesasade ningcriterionforSWSexmembershipnolongervalid.Thestatisticsofthecataclysmicvariablepopulationinthevicinityoftheupperperiodgapisalsodiscussed.

Keywords:accretion,accretiondiscs–binaries:close–stars:inpidual:HLAqr,BOCet,V849Her,V393Hya,AHMen,V380Oph,LQPeg,AHPic,V992Sco,LNUMa–novae,cataclysmicvariables

1INTRODUCTION

Thetheoryofcataclysmicvariable(CV)evolutionpredictsanabruptcessationofmasstransferatanorbitalperiodof～3h,i.e.theupperboundaryoftheperiodgap,wheremagneticbrakingisbelievedtobeinterrupted.However,itisbecomingincreasinglyclearthattheupperedgeofthegapisoverpopulatedbyCVswhichshowunusualbehaviour.Thesesystems,collectivelyknownastheSWSextantisstars(Thorstensenetal.1991),showanumberofcommonprop-erties,includinguncommon“V”-shapedeclipsepro les,the

presenceofHeIIλ4686emission,substantialdelaysoftheradialvelocitiesoftheBalmerandHeilineswithrespecttothemotionofthewhitedwarf,single-peakedemissionlinesthatdisplaycentralabsorptiondipsaroundorbitalphases 0.4 0.7,andhigh-velocityemissionS-waveswithmaxi-mumblueshiftnearphase～0.5.Theseobservationalcharac-teristicsdonoteasily tintothepictureofasteady-state,hotoptically-thickaccretiondiscwhichisexpectedtobecommoninintrinsicallybright,weakly-magneticCVsabovetheperiodgap.

Intermsofnumbers,theSWSexstarscurrentlyrepre-senthalfthetotalpopulationofnova-likesinthe3 4hor-bitalperiodrange(Rodr´ guez-Gil2005,Aungwerojwitetal.

E-mail:prguez@iac.es

[Abridged] We report on time-resolved optical spectroscopy of ten non-eclipsing nova-like cataclysmic variables in the orbital period range between 3 and 4 hours. Of the ten systems so far observed, HL Aqr, BO Cet, AH Men, V380 Oph, AH Pic, and LN UMa are

2P.Rodr´ guez-Gil,L.Schmidtobreick,B.T.G¨ansicke

2005,Rodr´ guez-Giletal.2007).Thus,theirstudyisofcrit-icalimportancetoinvestigatetheevolutionofCVsastheyenterthegap.

Manydi erentideashavebeenproposedtomodeltheunusualbehaviouroftheSWSexstars,butnoneofthemhasbeenabletoexplaintheSWSexphenomenoninfull.Amongthemanymechanismssofarinvokedwehighlightstreamover ow(Hellier&Robinson1994;Hellier1996),magneticaccretion(Rodr´ guez-Giletal.2001;Hameury&Lasota2002),magneticpropelleranchoredintheinnerdisc(Horne1999),andself-obscurationofthein-nerdiscbya aredouterdisc(Kniggeetal.2000).

InordertoaddresstheactualimpactoftheSWSexphenomenononthenova-likepopulationfoundbetween3and4hours,westartedtosearchforcharacteristicSWSexfeaturesinpoorly-studiednova-likesofbothhemispheresinthatperiodrange.Sincethemajorityofthesepropertiesareactuallyspectroscopicwewillentirelyfocusonphase-resolvedopticalspectroscopy.Thispapercontainsthe rstresultsofthisproject.

2

OBSERVATIONALDATAANDTHEIRREDUCTION

Time-resolvedspectroscopyofthecandidateSWSexstarswascarriedoutwiththeNewTechnologyTelescope(NTT)attheEuropeanSouthernObservatoryonLaSilla,andtheWilliamHerschelTelescope(WHT)attheRoquedelosMuchachosObservatoryonLaPalma.AttheNTTtheEMMI(ESOMulti-ModeInstrument)wasusedintheMediumDispersionSpectroscopymodewithgratingD/7centeredonHαandthe2048×4096pixel2MIT/LLCCDdetector.Ausefulwavelengthrangeofλλ6170 6900at0.8 Aspectralresolution(fullwidthathalfmaximum,FWHM)wasobtainedwitha1.0-arcsecslitwidth.

Thedouble-armedISISspectrographwasusedtoper-formtheobservationsattheWHT.TheblueandredarmswereequippedwiththeR600BandtheR316Rgratings,respectively.Thewavelengthrangesλλ3700 5045andλλ6230 8900weresampledat1.8 Aand3.3 Aresolution(FWHM;1.0-arcsecslit)onthe2048×4200pixel2EEV12andthe2148×4700pixel2MarconiCCDsintheblueandthered,respectively.Spectraofarclampswereregularlytakeninorderto …… 此处隐藏：44213字，全部文档内容请下载后查看。喜欢就下载吧 ……